在php 5.2版本中，openssl這個擴展的應用非常廣泛，它提供了安全的加密通信協議和數據加密處理功能，也可以用于創建和驗證數字證書，具有廣泛用途和靈活性。比如：

//從字符串中生成一對公私鑰
$config = array(
"private_key_bits" =>1024,
"private_key_type" =>OPENSSL_KEYTYPE_RSA,
);
$res = openssl_pkey_new($config);
openssl_pkey_export($res, $privkey);
$pubkey  = openssl_pkey_get_details($res);
$pubkey  = $pubkey["key"];
//進行數據的加密和解密等操作
$data = "hello openssl";
$encrypted = '';
$decrypted = '';
//加密
openssl_private_encrypt($data, $encrypted, $privkey, OPENSSL_PKCS1_PADDING);
//解密
openssl_public_decrypt($encrypted, $decrypted, $pubkey, OPENSSL_PKCS1_PADDING);
echo $decrypted; // "hello openssl"

openssl擴展提供了很多簡單易用的加密和解密函數，比如使用openssl_encrypt函數可以方便地對數據進行加密，示例代碼如下：

$data = "hello openssl";
$password = "password";
$method = "aes-128-cbc";
$iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length($method));
$encrypted = openssl_encrypt($data, $method, $password, 0, $iv);
$decrypted = openssl_decrypt($encrypted, $method, $password, 0, $iv);
echo $decrypted; //"hello openssl"

在網站開發中，我們有時會使用到ssl證書，用于實現https加密傳輸和驗證網站身份等操作。使用openssl擴展中的函數可以快速創建和驗證數字證書，比如：

//生成自簽名證書
$dn = array(
"countryName" =>"CN",
"stateOrProvinceName" =>"Beijing",
"localityName" =>"Haidian",
"organizationName" =>"PHP",
"commonName" =>"localhost",
);
$privkey = openssl_pkey_new();
$cert = openssl_csr_new($dn, $privkey);
$cert = openssl_csr_sign($cert, null, $privkey, 365);
openssl_x509_export($cert, $certout);
//驗證數字證書是否合法
$x509 = openssl_x509_read($certout);
$cinfo = openssl_x509_parse($x509);
if ($cinfo) {
echo "證書信息\n";
echo "=================================\n";
echo "公共名稱: " . $cinfo["subject"]["CN"] . "\n";
echo "頒發者: " . $cinfo["issuer"]["CN"] . "\n";
echo "有效期開始時間: " . date("Y-m-d H:i:s", $cinfo["validFrom_time_t"]) . "\n";
echo "有效期截止時間: " . date("Y-m-d H:i:s", $cinfo["validTo_time_t"]) . "\n";
echo "=================================\n";
}

除了以上應用，openssl擴展還可以用于數字簽名、哈希處理、隨機數生成等操作，非常方便實用。